Container surface and method of obtaining same

ABSTRACT

Vendability of nestable, resilient, plastic containers is improved by coating outside surface portions with a lubricant. These portions preferably are the nesting means and/or the lower sidewall area of the container. A process is provided for depositing the lubricant on the container which, in the case of a partially foamed container, may occur simultaneously with its exposure to a foaming agent.

'lJnited States Patent 1 Sincock [4 1 Oct. 36, 1973 CONTAINER SURFACEAND METHOD OF OBTAINING SAME [75] Inventor: Thomas F. Sincock, Simsburg,

Conn.

[73] Assignee: Ilikon Corporation, Natick, Mass.

[22] Filed: Oct. 30, 1970 [21] Appl. No.: 85,358

Related US. Application Data [62] Division of Ser. No. 760,911, Sept.19, 1968,

abandoned.

[52] US. Cl ll7/5.5, ll7/8.5, 117/38, 117/94, 117/161 ZA, 117/138.8'UA

[51] Int. Cl 844d 1/52 [58] Field of Search 117/8.5, 5.5,161 ZA, 117/155UA,10,11, 94, 98; 220/97 C;

[5 6] References Cited UNITED STATES PATENTS 3,374,922 3/1968 Shelby220/97 C 3,216,882 11/1965 Feldt et a1 117/98 X 3,013,306 12/1961 Richieet a1 264/121 X 3,144,971 8/1964 Wommelsdorf... 117/94 UX 3,262,6257/1966 Russell et a1 229/15 B 3,389,199 6/1968 Bushnell et a1. ll7/8.5 X

Primary ExaminerWilliam D. Martin Assistant ExaminerTheodore G. DavisAttorney-George H. Gerstman [57] ABSTRACT Vendability of nestable,resilient, plastic containers is improved by coating outside surfaceportions with a lubricant. These portions preferably are the nestingmeans and/or the lower sidewall area of the container. A process isprovided for depositing the lubricant on the container which, in thecase of a partially foamed container, may occur simultaneously with itsexposure to a foaming agent.

41 Claims, 4 Drawing Figures PAIENIEDum 30 ms FIG. I

SHEET l U? 5 CONTAINER SLIDE LINE INVENTOR THOMAS F. SINCOCK 'IIATTORNEYPATENTED OCT 30 I973 SHEET 2 or 5] FIG. 3

INVENTOR THOMAS E SINCOCK BY z 7 ATTORNEY PATENTED 0m 30 1973 SHEET 30F5 INVENTOR THOMAS F. SINCOCK ATTORNEY FATENIEUBBI 30 ms 3.769.056 SHEETNF 5 FIG. 4b

INVENTOR THOMAS E SINCOCK ATTORNEY PATENTED HBT 3 0 I975 SHEET 5 BF 5FIG. 4d

' INVENTOR THOMAS F. SINCOCK TTORNEY Y CONTAINER SURFACE AND METHOD OFOBTAINING SAME This is a division of copending application Ser. No.760,911, filed Sept. l9, 1968, and now abandoned.

This invention relates to containers and more particularly to nestablecontainers for use in coin operated dispensing machines.

Thin wall containers made of non-foamed as well as of entirely andpartially foamed plastic, such as those described in U.S. Pat. No.3,374,922, are being increasingly used in vending machines forcontaining hot and cold beverages of all types. These containers usuallyhave stacking or nesting means formed in a wall portion thereof whichfunction to maintain adjacent walls spaced from each other when a numberof such containers are nested together to form a stack. The stackingmeans usually comprises a series of cooperating shoulders or shelveshaving close dimensional tolerances, since these portions must beaccurately and consistently reproduced with a minimum of variation orotherwise the supported surface of the stacking means of one containermay proceed beyond the supporting surface of the stacking means of animmediately adjacent nested container during stacking or in subsequenthandling of a plurality of such containers. This results in a wedgingtogether of two or more containers, with the result that they do notconsistently feed freely from a nested relationship within a vendingmachine when a coin is inserted therein by a customer. Such hightolerance requirements often result in numerous container rejects,thereby lowering the economics of a high speed, large volume containerproducing operation.

This problem of nestable container vendability is aggravated with themore recently developed type container having a foam band integrallyalong its sidewall for insulating purposes. During formation of thisfoam covering, the portion of the container which is not to be foamed isusually masked to prevent the foaming agent from contacting it. However,in high speed production operations, foam breakthrough often occurs inthe container portion which is to be non-foamed. This foam has anunusually high coefficient of friction, and since portions of thenon-foamed surface are usually those which contact the next adjacentcontainer within the stack, as well as chute surfaces within the vendingmaching during movement of the container into its filling position,vendability of this type of container as limited by minute patches offoam breakthrough presents an unusual problem. In addition, in theprocess of producing these containers, masking is usually carried out bycoating the surface to be non-foamed with a chemical composition, suchas that set out in copending application Ser. No. 695,359, filed Jan. 3,1968, now US. Pat. No. 3,565,660, and assigned to the assignee of thepresent invention. The non-volatile portion of this composition whichremains on the surface of the container after foaming also has acoefficient of friction which is greater than that of the basic plasticsubstrate, and thus also tends to retard swift movement of the containeralong surfaces with which it comes into sliding contact.

Now there has been developed for use with either a non-foamed, partiallyfoamed or entirely foamed nestable container of the type used in vendingmachines, means for improving behavior of such containers within a stackand for reducing frictional resistance of these containers when insliding contact with the internal surfaces of automated vendingmachines.

Accordingly, it is a principle object of this invention to improve thevendability of nestable containers.

lt is another object of this invention to provide a container havingimproved resistance against wedging within another container when aplurality of like containers are nested together within a stack.

it is an additional object of this invention to reduce the frictionaleffect between surfaces of a vending machine and a plastic container incontact with the surfaces.

It is a further object of this invention to provide a containerexhibiting improved stacking performance yet permitting a relaxation ofthe tolerances of the stacking means by which the nesting isaccomplished.

It is an additional object of this invention to provide an improved,partially foamed, nestable and vendable container as well as a method ofproducing such a container.

It is a still further object of this invention to decrease thefrictional effects of a foamed surface on vendability of a partially orcompletely foamed, nestable container.

It is an additional object of this invention to decrease the effects offriction on vendability of a previously chemically masked portion of apartially foamed container.

It is yet a further object of this invention to provide a container anda method of forming such a container which overcomes the prior artdifficulties discussed above.

Other object of this invention will in part be obvious and will be partappear hereinafter.

These and other objects are accomplished by providing, in the broadestaspect of the invention, a nestable, thin wall, cup-like thermoplasticcontainer having nesting means formed in its sidewall for maintainingthe sidewall spaced from that of a similar container when nested therewithin, the sidewall having on at least a portion of its outer surface,a thin coating of lubricant to reduce frictional resistance to slidingbetween the coated surface and a supporting surface with which it comesinto contact.

In a preferred embodiment of the invention, the sidewall of the nestablecontainer has a gripping portion of major extent having a foamed, slipresistant covering on its outer surface, a lower, non-foamed sectionintermediate the base and the gripping portion, and an upper, non-foamedsection intermediate the gripping portion and the upper end, the upperand lower nonfoamed sections having portions off-set laterally withrespect to the gripping portion defining points of contact between thecontainer and a planar surface when the non-foamed sections are placedagainst said surface with the foamed slip resistant covering locatedinwardly of this surface, nesting means formed in the sidewall formaintaining the foamed, gripping, slip resistant surface of the sidewallof the container spaced from the sidewall of a similar container whennested therewith, the outer surface of the lower section having acoating of lubricant thereon to enhance sliding contact of the containeralong the planar surface.

A method is provided for forming the previously mentioned partiallyfoamed plastic container having a predetermined, lubricated, non-foamedexternal surface portion which comprises: masking a portion of thesurface of a plastic container which is to be nonfoamed; exposing atleast part of the masked portion along with another surface portion ofthe container which is to be foamed to a medium which is absorbable bythe plastic and convertible-to a gaseous state below the melting pointtemperature of the plastic used to form the container; heating theplastic container to a temperature below the melting point temperatureof the plastic but above the temperature at which the medium converts tothe gaseous state to produce a foam covering having a boundary along theedge of one of said surface portions; and applying a thin coating oflubricant to at least a portion of the external surface of the containerportion to be non-foamed.

In a preferred form of the method, the lubricant is dissolved in theabsorbable medium and coated on the masked surface at the same time theportion to be foamed is exposed to the absorbable medium.

In describing the overall invention, reference will be made to preferredembodiments depicted in the accompanying drawings in which:

FIG. 1 is a perspective view of a container embodying the presentinvention;

FIG. II is a partially sectioned, elevational view taken along the axisof the container of FIG. I;

FIG. III is a partial, sectional view of two nested containers of thetype shown in FIGS. I and II; and

FIG. IV is a diagrammatical view illustrating the operational steps forproducing the container of FIGS. I and II.

With reference to the drawings, wherein identical numerals refer toidentical parts, there is shown in FIGS. I-III a thin wall, nestable,cup-like thermoplastic container for beverages, foods and the like,which is of the throw-away type and is broadly identified as 10.Container generally comprises base 12, sidewall 14 generally extendingupwardly and outwardly from base 12 in a frustro-conical manner, formingopen upper end 17 at the free end of sidewall 14. Sidewall 14 comprisesmiddle finger gripping portion 16 having a relatively even outer surfaceof major extent, which diverges outwardly relative to the container axisat a substantially constant angle. The length of finger gripping surface16 may range between about 40 to 90 percent of the sidewall axiallength. Though notessential, surface 16 may have a partially foamedouter covering 18, obtained in a manner to be hereinafter described.Sidewall 14 further comprises lower section 20 intermediate base 12 andgripping surface 16, and upper section 22, intermediate gripping surface16 and open upper end 17.

Upper section 22 has portions offset from the angle of gripping surface16 to define nesting means formed therein, which, together with a cornerchime 40 at the peripheral joint between lower section 20 and base 12,cooperate with similar structure in a like container as illustrated inFIG. III, to maintain a radial clearance between the sidewalls of twoadjacently nested containers.

Nesting means of upper section 22 of sidewalll4 comprises outwardlyflaring arcuately spaced supporting shoulder 24', the upper edge ofwhich integrally merges into an upwardly and inwardly inclined spacingskirt 26. Spacing skirt 26 is integrally formed with an upwardly andoutwardly formed stacking shoulder 28 along its upper margin. As shownin FIG. III the point of integral adjoinment of stacking shoulder 28 andspacing skirt 26 forms an annular stacking edge 30. Stacking shoulder 28integrally merges at its upper end into an upwardly extending sidewallportion 31. Rim 32 flares outwardly and consists of an upper rim formingwall 34 which merges into reversely bent flange 36, thereby defining anouter rim margin 38 as typically shown in FIGS. II and III.

Slide line 54 of container 10 as depicted in FIG. II,

' is defined by a plane tangent at one point to the outer surface of thecontainer at the point of maximum diameter in an upper section above themidpoint of the sidewall, and at another point tangent to the outersurface of the radially outermost extremity of the section of thecontainer below the sidewall midpoint. These points need not necessarilybe at the upper sidewall extremity or at the lower joint between thesidewall and base though they are located at these points in theembodiment of FIGS. l-III. Corner chime as used herein is meant toinclude the radially outermost extremity of the lower end of thecontainer. In FIG. ll, slide line 54 is represented by a plane tangentto outer rim margin 38 of upper section 22, and to the outside surfaceof corner chime 40 of lower section 20.

In the form of the invention depicted in FIGS. H", the annularlyextending foam covering 18 of sidewall 14 extends from aboutthree-eighths inch above corner chime 40, to about one inch below itsuppermost peripheral margin. By further reference to FIG. II, and slideline 54, it can be seen that foamed section 18 of container 10 isradially inward of slide line 54, and is so located along the sidewallthat it will never come in contact with a straight surface against whichthe container is placed. Consequently, a container 10 passing along theinclined dispensing tube of a vending machine will never contact thewall of the dispensing tube except tangentially at corner chime 40 andouter rim margin 38.

In accordance with the present invention, container 10 has on at least aportion of its outer surface, a thin adherent coating 19 of a lubricantsuch as silicone oil, which functions to reduce the frictionalresistance between the coated surface and any other surface with whichit comes into sliding contact, such as the inner surface(s) of anadjacently stacked container or any of the surface(s) of the cupdispensing portions of an automated vending machine. Lubricant 19 in theembodiment of FIGS. I III is present on the outer surface of the nestingmeans in the upper portion 22 of the container sidewall between the topedge of the foamed gripping portion 18 and rim 32, on the lower portionof the sidewall 20 between the base 12 and the lower end of foamcovering 18 including chime 40 and also on the outer surface of themargin of base 12.

In use, container 10 is readily adaptable to be nested or stackedtogether with a plurality of like containers in the manner depicted inFIG. III. When placed in nested position, it can be seen that the outersurface of supporting shoulder 24 is engaged by the annular stackingedge 30 of stacking shoulder 28.

In the event of the tendency of the inner non-foamed surface of an outercup to move inward toward the foamed surface portion of the inner cup orvice versa, because for example, of a drag movement during transfer ofnested stacks within the vending machine, nonfoamed, outer anti-rubcorner chime 40 of the inner cup will contact the non-foamed innersurface of the bottom section of the outer cup as depicted in FIG. III,to maintain the desired sidewall clearance of the foamed portion of theinner cup from the non-foamed portion of the outer cup. Contact betweenthe chime and the inner surface of the next adjacent cup is in anedgewise manner rather than surface to surface, in order to minimizefrictional drag between the nonfoamed portions of the lower sections.

Lubricant film 19 is interposed (FIG. Ill) between the outer surface ofsupporting shoulder 24 of the inner container and the inner surface ofstacking edge 30 of the outer container in the limited peripheral areasof contact in the upper sidewall portions of each. Lubricant 19 islikewise disposed between the outer and inner surfaces of immediatelyadjacent stacked containers at the lower contacting portions of thesidewalls. When it is desired to release the lowermost container (or toraise the uppermost container) from a stack of a plurality of similarlyconstructed units, the lubricant film acts in a sense like a ballbearing to insure uniform and rapid separation of the outer and innercontainers around the peripheries of each at their upper ends, i.e.,between edge 30 of the outer container and shoulder 24 of the innercontainer. Lubricant 19 also functions to minimize the frictionalresistance against sliding of the inner surface of sidewall 18 of anouter cup along chime 40 at the lower end of the sidewall of the innercup as the outer cup moves away from the stack. Since the lubricantutilized must in all cases bear approval for use with comestibles by theFood and Drug Administration, trace amounts of the lubricant appearingon the inner surfaces of a container, which may have been rubbed off ofthe outer surface of an adjacent stacked unit are not objectionable fromthe standpoint of food or beverage contamination.

Container must subsequently fall by gravity along an inclined chute froma lower position within a nested stack in the upper section of anautomated vending machine into place in the filling station below.Contact during travel along the chute, which may not be entirely smooth,is along slide line 54. In so doing, lubricant 19 on chime 40 in thelowermost portion of the sidewall again aids in reducing frictionalresistance to sliding, thereby facilitating rapid and trouble freemovement of the cup into its dispensing position within the machine.

Referring now to FIG. IV, an expeditious process is illustrated by whicha partially foamed, plastic container having a predetermined,lubricated, non-foamed external surface portion is obtained.

Initially, a solution 60 is prepared (FIG. IVa) of a non-volatilelubricant 61 dissolved in a medium which is absorbable by the plasticand convertible to a gaseous state below the melting point of theplastic of the container being treated. The solution may be stirred bymeans of a suitable stirrer 64 in tank 65 to insure completedissolution. A completely non-foamed thermoformed cup 62 of the typedepicted in FIG. I is obtained, which it is desired to lubricate and topartially foam by providing previously described foam covering 18 alongthe major extent of its sidewall. To prevent absorption of the foamingagent into the plastic in the predetermined portions to be non-foamed,i.e., the upper and lower portions of the sidewall on either side of thefoam band, these portions are coated with a chemical lacquer compositioncomprising a non-volatile resinous ester dissolved in an alcohol asdescribed in copending application S er. No. 695,359 filed .Ian. 3,1968, now U.S. Pat. No. 3,565,660, and assigned to the assignee of thepresent invention. This coating is accomplished by moving cup 62 intocontact with a porous material 64 which is saturated with the chemicalmasking agent. The chemical masking agent is supplied to porous material64 by means ofa conduit connecting to a pressurized supply source of thecomposition. Porous applicator material 64 is supported in holder 66.Cup 62 is rotated as depicted at (b) while its upper and lower surfacesare in contact with porous material 64, thereby resulting in a coatingof the exterior of the bottom chime and the nesting means with thechemical masking composition, as well as the areas immediately adjacentthereto. The chemical masking agent utilized is considered to a liquidwhich when coated on the surface of the plastic and dried thereon toevaporate the solvent when the masking agent is a lacquer, acts as abarrier against absorption into the plastic of the absorbable foamingagent. The cup, having preselected exterior portions thereof coated withthe chemical masking agent, is then immersed in tank 65, which containsthe solution of lubricant dissolved in the absorbable medium, asschematically depicted at (c) for a predetermined interval of time. Atthe end of this interval of time, cup 62 is withdrawn from tank 65 andsubjected to a heat source as depicted at (d) which involves circulatinga fluid, e.g., air or steam at elevated temperature through an inletconduit 68 into the interior of cup 62. The heated fluid exits from thecup through outlet conduit 70 which has a diameter greater than that ofinlet conduit 68, and which is equipped with a flange 72 adpated to restagainst the upper surface of the rim of cup 62 while the gas is beingcirculated. The heat, which as shown is applied to the inner side of thecup, i.e., that which is opposite to the side which had been exposed tothe absorbable medium, results in the formation of foam covering 18along the area which was previously in contact with the medium and whichhad not initially been coated with the chemical masking agent. The cup62 is shown at (e) with the foam covering thereon.

Also, as a result of exposure to the solution of lubricant andabsorbable medium, a coating 19 of lubricant is left on top of thepreviously chemically masked upper and lower portions of the sidewall,on the nesting means and on the comer chime portions thereof. Thelubricant is also present on the surface of the plastic portion whichwas subsequently foamed, and therefore results in the lubricant beinginterspersed throughout the foam cells after the foaming step. Lubricant19 functions as previously described to enhance the stack release andvending properties of cup 62. Since the chemical masking agent isinsoluble in the solution of lubricant and absorbable medium, thenonvolatile portion of the masking agent is not disturbed from its placeas a coating on the preselected portions of the container sidewallduring the exposure step. Since the lubricant is relativelynon-volatile, it remains on the cup surface and does not evaporate asdoes the absorbable medium during the heating step.

The above description and particularly the drawings are set forth forpurposes of illustration only and should not be taken in a limitedsense.

The following examples are given to illustrate the invention and are notintended as limitation thereof. Unless otherwise specified, quantitiesare mentioned on a weight basis.

EXAMPLE 1 A solution of lubricant dissolved in a liquid foaming agentwas prepared by adding ten parts of liquid Dow Coming DC 200 siliconeoil (polydiemethyl siloxane characterized by a viscosity of 500centistokes, a specific gravity of 0.973 at 25 C. and a surface tensionof 21 dynes/cm. at 25 C.) to 1990 parts of Freon-l l(trichloromonofluoro methane). The mixture was stirred until a clearhomogeneous solution was obtained.

A rubber-modified styrene polymer blend having a Staudinger molecularweight of approximately 50,000, i.e., a physical blend of 7.5 parts ofstyrene-butadiene graft copolymer with 92.5 parts of styrene polymerwherein the graft copolymer contains 28 percent by weight of styrenebased on the weight of the copolymer, was thermoformed into a smooth,tapered cup approximately 4 inches in height and having an averageinside diameter of 2 inches. The cup had nesting means formed in theupper sidewall portion thereof similar to that depicted in FIG. I.

the cup were increased several fold. The foam was of excellent quality,the cells being fine in size and uniform inappearance.

Additional cups were thermoformed as set out above for test purposes tobe hereafter described. Certain of these cups were chemically masked andfoamed as set out above, except that the lubricant was not added to theFreon-l1 foaming agent. The entirely non-foamed cups, the partiallyfoamed, non-lubricated cups and additionally prepared cups partiallyfoamed and lubricated in the manner set out above, were passed down aninclined hollow cylindrical chute of the type utilized in automatedvending machines, which made an angle with the horizontal of about 60,and observed for speed relative to each other. The following resultswere w obtained. Numbers refer to the quantity of cups falling into thecategories identified by the key below.

Cup Chute Speed Percent of cup total in each category Cup identificationFL S A F FL S A F Unmasked, entirely nonfoamed O 12 55 A 0 0 17.9 82.1Chemically masked and partially foamed i0 24 25 18 13.0 3L2 32.4 23.4Chemically masked, lubricated and partially foamed... 0 0 16 55 0 0 22.677.4

FL Failurecup did not slide down chute. S Slow potential trouble.

A Adequate speed.

F-Fast-excellent vendability,

The iip frhied' by the a ave"aessfiaa s ssaaar was coated by contacting1 inch of the lower outer portion of the cup sidewall as well as theouter surface of the nesting means in the upper portion of the cupsidewall with a porous pad saturated with a resinous ester dissolved inalcohol. This latter composition was prepared by adding 35 parts byweight of Amberol 750 (a resinous ester formed by esterifying thereaction product of maleic anhydride and rosin acid with glycerol) to 60parts of methanol. After a 3 second interval the cup was separated fromcontact with the pad and The cup, chemically masked in this manner, wasthen immersed in the previously prepared solution of polydimethylsiloxane and Freon-l 1 up to within about onehalf inch of the top of thesidewall. The cup was maintained in this immersed condition for a periodof seconds after which it was withdrawn from the solution. After asecond interval at dry room temperature conditions, hot air at atemperature of 250 F. was circulated through the interior of the cup fora period of 10 seconds. W

The resulting had a foamed outer surface throughout the area ofimmersion in the solution of foaming agent and lubricant, extending intothe body of the cup for approximately one-third of its overallthickness, except for those portions of the cup which had beenpreviously coated with 'the resinous ester masking composition. Theselatter preselected portions were non-foamed and had a thin coating ofthe polydimethyl siloxane lubricant deposited thereon. Examination ofthe cup disclosed that its overall structural properties were notseriously altered by the steeping operation while at the same time theinsulating properties of be seen from the above, l00 perc ent of thechemically masked, lubricated, partially foamed cups tested wereconsidered to have adequate or better speed while sliding down thevending tube, with about 77 percent of this category considered to havefast speed, thereby producing excellent vendability. Results wereslightly better with the unmasked and non-foamed control cups andsubstantially poorer with the chemically masked and partially foamedcups.

EXAMPLE II A solution of lubricant dissolved in a liquid foaming agentis prepared by adding thirty parts of liquid Dow Corning DC 200 siliconeoil to 1970 parts of Freon-l l. The mixture was stirred until a clearhomogeneous solution was obtained. Chemical masking, exposing, foamingand testing are carried out in the same manner as in Example I utilizingsimilarly shaped initially thermoformed cups. Substantially equivalentresults are obtained.

In general, the plastics used in the practice of this invention aresubstantially thermoplastic materials which have been fabricated intocontainers having nesting means simultaneously formed therein, andinclude such materials as polystyrene, styrene-buta-dieneacrylonitrilegraft and/or mechanical polyblends, other rubber-modified graft andmechanically blended styrene polymers, vinyl chloride, vinyl acetatecopolymers, polyethylene, chlorosulfonated polyethylene, chlorinatedpolyethylene and ethylene-vinyl acetate copolymers which are graftand/or mechanically blended with polyvinyl chloride homopolyrners andcopolymers, polyvinyl halide homopolymers and copolymers includinginterpolymers, mixtures and plasticized versions of the same.

The plastic solvent foaming agent may be any material which is (1) atleast a partial solvent for the plastic being processed, and (2)convertible to a gaseous state at a temperature below the melting pointtemperature of the plastic. Freon-l l (trichlorofluoromethane) isgenerally preferred for polystyrene homopolymers and rubber-modifiedinterpolymers, with methylene chloride, acetone, dichloro-ethylene,xylene, carbon tetrachloride, methyl ethyl ketone, benzol, toluol,chloroform and the like being likewise effective depending on theparticular plastic being used.

The masking step of the above-described process of the present inventionmay be achieved by either coating with a chemical composition as setforth in the preferred embodiment or by mechanical means. Typical of thelatter approach is the use of a sealed chamber imposed around the cupsurface(s) to be non-foamed to shield these portions during exposure ofthe cup to the absorbable medium. Also useful for effective masking arethe utilization of cooled surfaces in contact with either side of thesurface to be non-foamed, while the surface to be foamed is heated. Thismay be accomplished by means of cooling rings in contact with theoutside surface portion of the cup which is to be nonfoamed or by meansof a composite mandrel placed against the wall of the interior of thecup prior to exposure to the absorbable medium, the mandrel having bothheated portions for creating foam and cooled portions for retardingfoaming.

In the preferred chemical masking approach the coating materialsemployed may be any fluid substances which will serve as a barrieragainst absorption of the medium by the plastic. The choice of the'fluidsubstance, utilized will, of course, depend on the medium employed inthe process. In some instances, it may be desirable to employ fluidsubstances which are considered insoluble in the particular mediumemployed. Preferentially, the coating composition is a lacquercomprising a resinous ester which is a derivative of rosin or rosinacids, a modified rosin or a modified tarpene hydrocarbon, which issoluble in alcohol and generally insoluble in aliphatic and petroleumhydrocarbons. This composition has been found to effectively shield theportions to be non-foamed from the absorbable medium. However, thenon-volatile resinous ester portion of the composition, afterevaporation of the solvent, is rather rough and slip resistant which, asmentioned, causes vending and stack separation problems with the cups.The problem is unusually overcome by the present invention wherein theseslip resistant surfaces are subsequently coated with a slip promotingtype of release agent during the exposure step.

Regardless of the manner in which the masking is achieved in the presentinvention, patches of almost imperceptible foam breakthrough oftenappear in the area of the cup which was meant to be non-foamed. This isespecially true in high speed production operations because ofincomplete masking, whether it be a result of a slight discontinuity inthe coating of chemical masking agent or incomplete shielding or surfacecontact if one of the other methods of masking is used. This foam, asmentioned, has a rather high coefficient of friction which may cause cupsliding problems. However, the effect of this deficiency is diminishedby the manner of coating of the preferred embodiment wherein a film oflubricant has already been deposited on the surface prior to the foamingstep when the patches are generated. Thus the present invention canreduce the criticality of the masking step since foam patch breakthroughis no longer as much of a problem.

In general, the plastic article is permitted to dry for a short intervalof time after exposure to the foaming agent lubricant solution and priorto heating. This drying interval allows deeper diffusion and serves toharden the outer surface of the cup somewhat, forming a skin which aidsconsiderably in the formation of the closed cell structures which arenecessary for good insulating properties. If desired, the drying,interval may be accelerated by forced air blasts, moderate heatingconditions, etc.

After the drying interval, the plastic article is heated to foam theoutermost portions of the plastic article. The heating means utilizedmay vary, the final results being affected by the uniformity of heating,rate of heating and temperature level at which it is conducted. Heatingmay be on either the same or the opposite side of the cup surface whichhad been exposed to the absorbable medium. An especially unifoml foamhas been obtained by exposing the side opposite to that which had beenexposed to the foaming agent.

Though it is preferred for operational simplicity to coat the containerportion to be non-foamed with the lubricant simultaneously withimmersion in the medium, any suitable equipment may be employed to coatthe portion of the plastic container to be non-foamed as a separate stepeither before or after exposure to the foaming agent. For example, thiscould even occur by utilizing a brush, roll or similar device eitherwith or without a partial foaming step.

The quantity of coating applied should be such that the dry coatingweight is from about 0.1 to 1.5 parts of lubricant per 98.5 to 99.9parts of liquid foaming agent, and preferably 0.1 to 0.5 parts oflubricant per 99.5 to 99.9 parts of foaming agent.

The lubricant utilized on the container surfaces of the presentinvention must have clearance of the Food and Drug Administration foruse in food packaging applications, since this is the type of containercontemplated by the invention. Consequently, it should be inert, clearand non-toxic, but may be either a solid or liquid at room temperatureconditions prior to dissolution. It must have the ability to reducefriction between the plastic container and another surface along whichthe container is sliding. When utilized in conjunction with the partialfoaming process wherein coating takes place during exposure to theabsorbable medium as in the preferred embodiment, the lubricant shouldbe miscible in the absorbable medium. It must be highly efficient at lowconcentrations,'be soluble in water or organic solvents and have noeffect on the quality of the foam produced during the heating step. Itshould be relatively non-volatile at temperatures up to about 200 C, inorder to avoid evaporating during the foaming step. Effective lubricantsinclude fatty materials such as fatty acids having from 8 to 24 C atoms,ethers, alcohols and amides such as oleamide, palmitamide, linoleamideand stearamide; polyethylene glycols having average molecular weights inthe range of between about 400 to 4,000; fully refined paraffin waxesmelting at between about to 180 F.; petrolatum, glycerine, castor oil,mineral oil, fluorocarbon polymers and fluorocarbon surfactants.Particularly preferred when the lubricant is applied during the partialfoaming process are polymeric silicone materials characterized by arepeating siloxane linkage, i.e.,

wherein R, and R are either C or C alkyl groups.

Polydimethyl siloxane is particularly preferred since it has been foundto have no effect on the quality of foam produced on the finishedcontainer, with the resulting cell size being equivalent to thatobtained without use of the lubricant. Also, off grade scrap cups havingthis type of lubricant coated on their surfaces showed no signs ofincompatibility or other adverse processing behavior when reground andre-extruded.

It should be noted that the present invention is applicable todeposition of lubricant on any exterior surface portion of a nestablecontainer of a type wherein it is desirable to increase its slidingproperties. it is preferred however that the coating be applied on thelower portion of the sidewall in the area of its joint with the base andon the surfaces of the nesting means. Satisfactory results are obtainedby coating at either or both of these sections of the cup.

As an advantageous side effect of the lubricated exterior surfaceportions of the containers of the present invention, it has been notedthat minor amounts of the lubricant are rubbed off the surfaces of thecups onto various cup supporting surfaces of the vending machines over aperiod of time. This also decreases the effect on cup dispensing speedof sticky internal surfaces of these machines which may be caused byvapors condensing from hot liquids within the machine which are presentas parts of the constituents of the beverage being dispensed.

The nestable containers of the present invention are formed fromresilient thermoplastic materials. The structures are used in coinoperated beverage dispensing machines and broadly where spacerequirements require that a plurality of containers be nested togetherwithin a stack. The lubricated surfaces of the invention are especiallyapplicable in insulated containers for holding hot or cold substanceshaving integral nonfoamed wall portions which provide improvedstructural properties. The invention is likewise applicable, however, toentirely foamed and entirely non-foamed containers.

it is obvious that many variations may be made in the products andprocesses set forth above without departing from the spirit and scope ofthe invention as hereinafter claimed.

I claim:

1. A method of forming a partially foamed, plastic container having apredetermined, lubricated, nonfoamed external surface portion whichcomprises:

a. dissolving a lubricant in a medium which is absorbable by the plasticand convertible to a gaseous state below the melting point temperatureof the plastic used to form the container, to form a solution oflubricant in the absorbable medium;

b. masking a portion of said foamable plastic container which is to benon-foamed;

c. exposing at least part of said masked portion along with anotherportion of said container which is to be foamed to said solution tosimultaneously coat said exposed masked portion with said lubricant andpermit said medium to be absorbed into the portion of the plastic to befoamed; and

d. heating the plastic container to a temperature below the meltingpoint temperature of the plastic but above the temperature at which themedium converts to the gaseous state to produce a foam covering having aboundary along the edge of one of said container portions.

2. The method of claim 1 wherein masking is accomplished by coating witha liquid chemical composition which is substantially insoluble in theabsorbable medium.

3. A method of forming a partially foamed, plastic container having apredetermined, lubricated, nonfoamed external surface portion whichcomprises:

a. dissolving a lubricant in a medium which is absorbable by the plasticand convertible to a gaseous state below the melting point temperatureof the plastic used to form the container, to form a solution oflubricant in the absorbable medium;

b. depositing a chemical masking composition which is substantiallyinsoluble in said absorbable medium on an outer surface portion of acontainer which is to be non-foamed;

entirely exposing said masked outer surface portion of said containeralong with another outer surface portion of said container to be foamedto said solution of lubricant in absorbable medium, to coat saidpreviously chemically masked surface portion with said lubricant to formsaid predetermined, lu-

bricated non-foamed external surface portion without the absorbablemedium portion of the solution dissolving said chemical maskingcomposition,

while concurrently permitting said absorbable medium to be absorbed intothe surface portion of the plastic to be foamed; and

d. applying heat to the inside of the container to cause said outersurface portion of the container which had absorbed said medium to foam.

4. The method of claim 3 wherein:

a. the masking composition is a resinous ester dissolved in alcohol;

b. the lubricant is silicone oil; and

c. the absorbable medium is trichlorofluoromethane.

Patent No. 3, 769,056 Dated October 30, 1973 Inv Thomas F. Sincock It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Columnl, line 46, "rnaching" should be machine Column 1, line 49, "of"should be for Column 2, line 30, "object" should be objects Column 2,line 31, "be" should be in Column 2, line 58, "therewith" should betherewithin Column 3, line 41, after "the", insert the word totel Column6, line 12, after to", insert the word be Column 9, line 41, "tarpene"should be terpene Signed and sealed this 30th day of April 197A.

(SEAL) Attes t:

EDWARD M .l LETCHEH, JR. C RSHALL DANN Attesting Officer Commissioner ofPatents FORM PO-105O (10-69) L!SCOMM-D C 60376-F'69 U.S. GOVERNMENTPRINTING OFFICE HI IB 0-365-334

2. The method of claim 1 wherein masking is accomplished by coating witha liquid chemical composition which is substantially insoluble in theabsorbable medium.
 3. A method of forming a partially foamed, plasticcontainer having a predetermined, lubricated, non-foamed externalsurface portion which comprises: a. dissolving a lubricant in a mediumwhich is absorbable by the plastic and convertible to a gaseous statebelow the melting point temperature of the plastic used to form thecontainer, to form a solution of lubricant in the absorbable medium; b.depositing a chemical masking composition which is substantiallyinsoluble in said absorbable medium on an outer surface portion of acontainer which is to be non-foamed; c. entirely exposing said maskedouter surface portion of said container along with another outer surfaceportion of said container to be foamed to said solution of lubricant inabsorbable medium, to coat said previously chemically masked surfaceportion with said lubricant to form said predetermined, lubricatednon-foamed external surface portion without the absorbable mediumportion of the solution dissolving said chemical masking composition,while concurrently permitting said absorbable medium to be absorbed intothe surface portion of the plastic to be foamed; and d. applying heat tothe inside of the container to cause said outer surface portion of thecontainer which had absorbed said medium to foam.
 4. The method of claim3 wherein: a. the masking composition is a resinous ester dissolved inalcohol; b. the lubricant is silicone oil; and c. the absorbable mediumis trichlorofluoromethane.